The invention relates to a process for determining the value of parameters which change the resonance frequency of microstructures.
In J. Microwave Power (1987) pages 85 to 93 various processes for contact-free temperature measurements of objects whose temperature is to be determined but which are not directly accessible are described. In each case a glass fiber is brought close to the object whose temperature is to be measured. By measuring the temperature-dependent fluorescence properties of a fluorescent substance disposed on the object to be measured the temperature at the measuring location can be deducted. These processes however have the disadvantage that a glass fiber has to be brought into close proximity, that is, to no more than about 10 mm, to the object to be measured.
U.S. Pat. No. 3,596,069 discloses a similar process by which the resonance frequency of a cylindrical body is determined. Herefrom the frequency determining parameters are obtained. Further, from the German Patent Publication De 30 12 774 A1 it is known to excite a test body with ultrasonic radiation, whereupon the amplitude of the resonance frequency is measured. From the deviation of the resonance frequency amplitude from a predetermined value, the presence of a defect within the body is determined.
British Patent Publication GB 21 43 036A describes a method for the detection of intergranular defects of test pieces wherein ultrasound echoes of perfect pieces are registered as standard values. A comparison of the ultrasound echoes of faulty test pieces with the standard value gives an indication of the degree of faultiness. However, this procedure is not suitable for thin membranes because the travel distances of the sound within the membrane are too short.
Another method of this type is known from the U.S. book "Ultrasonic Testing" published by F. Szilard, 1982, pages 432-436.
Finally, in the Journal of the Acoustical Society of America, Vol. 80, No. 6, December 1986, pages 1762 to 1776, the resonance scattering of ultrasound in various layers is described.
It is the object of the present invention to provide a process which facilitates measurement of temperatures, expansion, pressures, densities, flow speeds, coating rates, internal mechanical strain and modules of elasticity of objects which are not directly accessible during measurement without the need for bringing circuit points or conductors in close proximity to the object to be measured during the measuring procedure.